JP2020125941A - Mask inspection device and focus adjustment method - Google Patents

Abstract

To provide a mask inspection device and a focus adjustment method for improving auto-focus performance when inspecting a mask and improving the accuracy of inspection.SOLUTION: A mask inspection device 1 pertaining to the present invention comprises: a field diaphragm 10b for EUV masks which emits illumination light having a beam B1b that includes circular polarized light, a beam B2b that includes P-polarized light and a beam B3b that includes S-polarized light; unpolarized light BS20b for reflecting a portion of illumination light L1b and passing a portion of reflected light R1b through; an objective lens 40 for condensing illumination light L1b and passing reflected light R1b through; a first and a second detector for detecting reflected light R1b; a half mirror 91; a light receiving part 92 arranged at a front pin position, for receiving the beam B1b having passed through the half mirror 91; and a light receiving part 93 arranged at a rear pin position, for receiving the beam B1b having been reflected by the half mirror 91.SELECTED DRAWING: Figure 4

Description

The present invention relates to a mask inspection device and a focus adjustment method, for example, a mask inspection device and a focus adjustment method for inspecting a defect of a photomask used in a semiconductor manufacturing process.

When inspecting an EUV mask with a mask inspection apparatus that inspects an EUV (Extreme Ultraviolet) mask, in order to improve the sensitivity of detecting a minute pattern, the inspection is performed using illumination light including linearly polarized light in mutually different directions. May be done.

Patent Document 1 describes illuminating a mask to be inspected by reflecting illumination light including first linearly polarized light and second linearly polarized light having different polarization directions by a half mirror.

On the other hand, in a mask inspection apparatus that inspects an optical mask, when the illumination light is reflected by a half mirror, a light amount loss occurs, and it may be difficult to secure the light amount of the illumination light necessary for the inspection. Therefore, by using a beam splitter and a λ/4 plate as the reflection illumination optical system, the mask to be inspected is illuminated with illumination light including circularly polarized light.

Patent No. 4701460 JP, 2009-223095, A Japanese Patent Laid-Open No. 05-109601 JP, 2013-024772, A JP, 2017-0093379, A JP, 2017-090147, A JP, 2014-048217, A JP-A-4-289409 JP, 2003-344306, A JP, 2009-216648, A JP, 2010-092984, A JP2012-127856A

In order to inspect an optical mask and an EUV mask with the same mask inspection apparatus, it is necessary to switch between a beam splitter and a half mirror, and insert and remove a λ/4 plate. However, due to such switching or the like, the polarization of the reflected light used for autofocusing also changes, which causes a problem such as deterioration of autofocusing performance. Further, if the reflected light used for autofocus is a predetermined linearly polarized light, in the half mirror that separates the front focus and the rear focus, the dependency of the reflectance due to the polarization has an influence, and the autofocus performance deteriorates.

An object of the present invention is to provide a mask inspection apparatus and a focus adjustment method capable of improving autofocus performance when inspecting a mask and improving inspection accuracy.

The mask inspection apparatus according to the present invention changes a polarization state of a part of the incident illumination light including the first linearly polarized light, and the first beam including the first linearly polarized light and the first linearly polarized light have different polarization directions. A field stop for an EUV mask that emits illumination light having a second beam including a second linearly polarized light and a third beam including a circularly polarized light, and the first linearly polarized light, the second linearly polarized light, and the circularly polarized light A non-polarization beam splitter that reflects a part of the light and transmits a part of the light including the first linearly polarized light, the second linearly polarized light, and the circularly polarized light, and the illumination reflected by the non-polarized beam splitter While converging light on the mask to be inspected, the first beam reflects the first beam from the mask to be inspected, the second beam reflects the second beam from the mask to be inspected, and the third beam An objective lens that transmits the reflected light having the third light reflected by the mask to be inspected, and the reflection that includes one of the first light and the second light that has passed through the objective lens and the non-polarization beam splitter A first detector for detecting light and a second detector for detecting the reflected light including the other; a half mirror for transmitting and reflecting the third light transmitted through the objective lens and the non-polarization beam splitter; A first light receiving portion arranged at a position to be a front focus of the image formed by the third light, for receiving the third light transmitted through the half mirror; and a position arranged to be a rear focus of the image formed by the third light, A second light receiving portion that receives the third light reflected by the half mirror. With such a configuration, the autofocus performance can be improved and the inspection accuracy can be improved.

Further, the focus adjusting method according to the present invention changes a polarization state of a part of the incident illumination light including the first linearly polarized light, and includes the first beam including the first linearly polarized light, the first linearly polarized light and the polarization direction. Emitting illumination light having a second beam including a second linearly polarized light different from each other and a third beam including circularly polarized light; concentrating the illumination light on an inspection target mask by an objective lens, and Reflected light having first light reflected by the mask to be inspected, second light reflected from the mask to be inspected by the second beam, and third light reflected by the mask to be inspected by the third beam To the objective lens, transmitting and reflecting the third light of the reflected light transmitted through the objective lens in a half mirror, and a position that becomes a front focus of the image by the third light. A step of receiving the third light transmitted through the half mirror by a first light receiving portion arranged in the step of: and a second light receiving portion arranged at a position to be a rear focus of the image by the third light, Based on the step of receiving the third light reflected by the mirror, the intensity of the third light received by the first light receiving section, and the intensity of the third light received by the second light receiving section Adjusting the position of the objective lens or the mask to be inspected. With such a configuration, the autofocus performance can be improved and the inspection accuracy can be improved.

According to the present invention, it is possible to provide a mask inspection apparatus and a focus adjustment method that improve autofocus performance when inspecting a mask and improve inspection accuracy.

6 is a diagram illustrating the configuration of an optical mask inspection apparatus according to Comparative Example 1. FIG. 7 is a diagram illustrating the configuration of an EUV mask inspection apparatus according to Comparative Example 2. FIG. It is a graph which illustrated the reflectance of P polarized light and S polarized light, and a horizontal axis shows an incident angle and a vertical axis shows reflectance. It is a block diagram which illustrated the mask inspection apparatus which concerns on embodiment. FIG. 3 is a plan view illustrating a field stop unit in the mask inspection apparatus according to the embodiment. FIG. 7A is a plan view illustrating illumination light that illuminates a pattern surface of a photomask in the mask inspection apparatus according to the embodiment, and FIG. 7B is a pattern of an EUV mask in the mask inspection apparatus according to the embodiment. It is a top view which illustrated the illumination light which illuminates a surface. It is a block diagram which illustrated the autofocus unit of the mask inspection apparatus which concerns on embodiment, and shows the case where an optical mask is inspected. It is a block diagram which illustrated another autofocus unit of the mask inspection apparatus which concerns on embodiment. It is a block diagram which illustrated the autofocus unit of the mask inspection apparatus which concerns on embodiment, and shows the case where an EUV mask is inspected. It is a flowchart figure which illustrated the method of inspecting a photomask in the mask inspection method which concerns on embodiment. It is a flowchart figure which illustrated the method of inspecting the EUV mask in the mask inspection method which concerns on embodiment.

Hereinafter, a specific configuration of this embodiment will be described with reference to the drawings. The following description shows preferred embodiments of the present invention, and the scope of the present invention is not limited to the following embodiments. In the following description, the same reference numerals indicate substantially the same contents.

First, Comparative Example 1 and Comparative Example 2 will be described. Thereby, the problems found by the inventor will be described. Then, an embodiment for solving the problem will be described.

(Comparative Example 1)
FIG. 1 is a diagram illustrating the configuration of an optical mask inspection apparatus according to Comparative Example 1. As shown in FIG. 1, the inspection apparatus 101a for the optical mask Ma includes a field stop 110a, a beam splitter 120a, a λ/4 plate 130, an objective lens 140, mirrors 151 and 152, and an autofocus unit 190. The autofocus unit 190 has a half mirror 191, and light receiving portions 192 and 193.

In the case of the inspection device 101a for the optical mask Ma, for example, the illumination light L101 including the linearly polarized S-polarized light is guided to the field stop 110a. The field stop 110a has a CAF slit 115a and a slit 116a. The illumination light L101a that has passed through the CAF slit 115a is called a beam B101a. The beam B101a becomes the illumination light L101a for autofocus. The illumination light L101a that has passed through the slit 116a is called a beam B102a. The beam B102a becomes the inspection illumination light L101a. The illumination light L101a emitted from the field stop 110a includes a beam B101a and a beam B102a. Both the beam B101a and the beam B102a include S-polarized light. The illumination light L101a is reflected by the beam splitter 120a.

The beam splitter 120a is, for example, one that reflects S-polarized light and transmits P-polarized light. P-polarized light is linearly polarized light that is orthogonal to S-polarized light. The illumination light L101a reflected by the beam splitter 120a passes through the λ/4 plate 130. Accordingly, the illumination light L101a including the S-polarized beam B101a and the beam B102a is converted into the illumination light L101a including the circularly-polarized beam B101a and the beam B102a.

The illumination light L101a converted to include circularly polarized light by the λ/4 plate 130 is condensed by the objective lens 140 and illuminates the photomask Ma. The reflected light R101a, which is the illumination light L101a reflected by the photomask Ma, passes through the objective lens 140. The reflected light R101a reflected by the light mask Ma includes circularly polarized light that is reverse in rotation to the illumination light L101a. That is, the beams B101a and B102a included in the reflected light R101a include circularly polarized light having a rotation opposite to that of the illumination light L101a.

The reflected light R101a including the circularly polarized light that has passed through the objective lens 140 is converted into the reflected light R101a that includes the P-polarized light by passing through the λ/4 plate 130. That is, the beam B101a and the beam B102a included in the reflected light R101a include P-polarized light. Therefore, the reflected light R101a including the beam B101a and the beam B102a passes through the beam splitter 120a.

The reflected light R101a transmitted through the beam splitter 120a includes an autofocusing beam B101a and an inspection beam B102a. The reflected light R101a including the inspection beam B102a is guided to a detector (not shown) by a predetermined optical member. The detector inspects the photomask Ma by detecting the beam B102a in the reflected light R101a.

On the other hand, the reflected light R101a containing the beam B101a for autofocus is guided to the autofocus unit 190 by the mirrors 151 and 152. Then, the reflected light R101a is transmitted or reflected by the half mirror 191. The light receiving unit 192 is arranged at a position that serves as a front focus of an image formed by the beam B101a. The light receiving unit 192 receives the beam B101a transmitted through the half mirror 191. The light receiving unit 193 is arranged at a position where the image formed by the beam B101a is back-focused. The light receiving unit 193 receives the beam B101a reflected by the half mirror 191.

Feedback control is performed so that the intensities of the beams B101a received by the light receiving unit 192 and the light receiving unit 193 are equal, and the objective lens 140 or the optical mask Ma is moved. As a result, the autofocus can be performed and the focus can be adjusted.

(Comparative example 2)
FIG. 2 is a diagram illustrating the configuration of an EUV mask inspection apparatus according to Comparative Example 2. As shown in FIG. 2, the inspection device 101b for the EUV mask Mb includes a field stop 110b, a non-polarizing beam splitter 120b, an objective lens 140, mirrors 151 and 152, and an autofocus unit 190. The autofocus unit 190 has a half mirror 191, and light receiving portions 192 and 193.

In the case of the inspection device 101b for the EUV mask Mb, for example, the illumination light L101 including the linearly polarized S-polarized light is guided to the field stop 110b. The field stop 110b has a CAF slit 115b, a slit 116b, and a slit 117b. A λ/2 plate is attached to the slit 117b.

The illumination light L101b that has passed through the CAF slit 115b is called a beam B101b. The illumination light L101b that has passed through the slit 116b is called a beam B102b. The illumination light L101b that has passed through the slit 117b is called a beam B103b. The beam B101b becomes illumination light L101b for autofocus. The beam B102b and the beam B103b become the illumination light L101b for inspection. The illumination light L101b emitted from the field stop 110b includes beams B101b, B102b and a beam B103b. Both the beam B101b and the beam B102b include S-polarized light. On the other hand, the beam B103b contains P-polarized light.

When inspecting the EUV mask Mb, the illumination light L101b containing S-polarized light and P-polarized light is used. As a result, it is possible to improve the detection sensitivity of minute patterns along the vertical and horizontal directions on the pattern surface of the EUV mask Mb. In order to reflect both S-polarized light and P-polarized light, the illumination light L101b is reflected by the non-polarized beam splitter 120b.

The non-polarization beam splitter 120b reflects a part of the S-polarized light and a part of the P-polarized light, and transmits a part of the S-polarized light and a part of the P-polarized light. The illumination light L101b reflected by the non-polarization beam splitter 120b is condensed by the objective lens 140 and illuminates the EUV mask Mb. The reflected light R101b obtained by reflecting the illumination light L101b on the EUV mask Mb passes through the objective lens 140.

The reflected light R101b reflected by the EUV mask Mb includes an S-polarized beam B101b and a beam B102b, and a P-polarized beam B103b. A part of the reflected light R101b transmitted through the objective lens 140 is transmitted through the non-polarization beam splitter 120b. The reflected light R101b that has passed through the non-polarizing beam splitter 120b includes an autofocusing beam B101b, and an inspection beam B102b and a beam B103b. The reflected light R101b including the inspection beam B102b and the beam B103b is guided to a detector (not shown) by a predetermined optical member. The detector inspects the EUV mask Mb by detecting the beam B102b and the beam B103b in the reflected light R101b.

On the other hand, the reflected light R101b including the beam B101b for autofocus is guided to the autofocus unit 190 by the mirrors 151 and 152. Then, the reflected light R101b is transmitted or reflected by the half mirror 191 as in the case of the optical mask Ma. The light receiving unit 192 is arranged at a position that serves as a front focus of an image formed by the beam B101b. The light receiving unit 192 receives the beam B101b that has passed through the half mirror 191. The light receiving unit 193 is arranged at a position where the image by the beam B101b is back-focused. The light receiving unit 193 receives the beam B101b reflected by the half mirror 193.

The objective lens 140 or the EUV mask Mb is moved by performing feedback control so that the beams B101b received by the light receiving unit 192 and the light receiving unit 193 have the same intensity. As a result, the autofocus can be performed and the focus can be adjusted.

In order to inspect the optical mask Ma of Comparative Example 1 and the EUV mask Mb of Comparative Example 2 with the same device, switching between the field stop 110a and the field stop 110b, and the beam splitter 120a and the non-polarizing beam splitter 120b. Will need to be switched. Further, it is necessary to replace the λ/4 plate 130. However, the switching also changes the polarization of the light used in the autofocus unit 190. Then, the autofocus performance may deteriorate.

Specifically, in the case of Comparative Example 1, the autofocus beam B101a for illuminating the photomask Ma contains circularly polarized light. On the other hand, in the case of Comparative Example 2, the auto-focusing beam B101b for illuminating the EUV mask Mb contains S-polarized light. Therefore, when the beam for autofocus illuminates a pattern such as a line and space, the angle of the beam with respect to the pattern changes by switching. As a result, the stability of autofocus is reduced due to the switching.

Further, in the case of Comparative Example 1, the autofocusing beam B101a incident on the half mirror 191 contains P-polarized light. On the other hand, in the case of Comparative Example 2, the auto-focusing beam B101b incident on the half mirror 191 contains S-polarized light. The reflectance of the half mirror 191 depends on the polarization depending on the polarization direction of the linearly polarized light. Therefore, the amount of light received by the light receiving units 192 and 193 changes.

FIG. 3 is a graph exemplifying the reflectances of P-polarized light and S-polarized light, where the horizontal axis represents the incident angle and the vertical axis represents the reflectance. As shown in FIG. 3, for example, when the beam B101a and the beam B101b are incident on the half mirror 191 at 45°, the reflectances are different. Therefore, the amount of light received by the light receiving unit 192 and the light receiving unit 193 changes due to the switching. Therefore, the switching reduces the stability of the autofocus.

(Embodiment)
<Structure of mask inspection device>
Next, the mask inspection apparatus according to this embodiment will be described. The mask inspection apparatus of this embodiment solves the problems of Comparative Example 1 and Comparative Example 2, for example. The mask inspection apparatus of this embodiment is, for example, a mask inspection apparatus that detects defects in a photomask used in a semiconductor manufacturing process. The mask inspection apparatus of this embodiment includes the optical mask Ma and the EUV mask Mb as inspection targets. For example, the inspection target can be switched from the photomask Ma to the EUV mask Mb, or from the EUV mask Mb to the photomask Ma. However, either one of the mask inspection devices may be used. FIG. 4 is a configuration diagram illustrating the mask inspection apparatus according to the embodiment.

As shown in FIG. 4, the mask inspection apparatus 1 includes a field stop unit 10, a beam splitter unit 20, a λ/4 plate 30, an objective lens 40, a mirror 50, a polarization splitting unit 60, and detectors 71 and 72. .. The mask inspection apparatus 1 may include the light source 80, and may include one or more optical members such as lenses and mirrors (not shown). The mask inspection apparatus 1 also includes an autofocus unit (not shown) described later.

The mask inspection apparatus 1 inspects, for example, a pattern defect of the optical mask Ma and the EUV mask Mb which are inspection targets. The EUV mask Mb is a mask that uses EUV light as exposure light, and the photomask Ma is a mask that uses exposure light having a wavelength longer than that of EUV light. Here, for convenience of description of the mask inspection apparatus 1, XYZ orthogonal coordinate axes are introduced. A plane parallel to the pattern surfaces of the photomask Ma and the EUV mask Mb is defined as an XY plane. The direction orthogonal to the pattern surface is the Z-axis direction. For example, the upper side is the +Z axis direction and the lower side is the −Z axis direction. The XYZ orthogonal coordinate axes are used to describe the mask inspection apparatus 1, and do not indicate the position when the mask inspection apparatus 1 is actually used.

The illumination light L1 that illuminates the mask to be inspected is, for example, laser light. The illumination light L1 emitted from the light source 80 enters the field stop unit 10 via an optical member such as a lens and a mirror. The illumination light L1 entering the field stop unit 10 contains linearly polarized light. For example, P-polarized linearly polarized light is included. P-polarized light is called first linearly polarized light, and S-polarized light is called second linearly polarized light. The field stop unit 10 controls the polarization state of the incident illumination light L1. The field stop unit 10 emits the illumination light L1 whose polarization state is controlled.

FIG. 5 is a plan view illustrating the field stop unit 10 in the mask inspection apparatus 1 according to the embodiment. As shown in FIG. 5, the field stop unit 10 includes a field stop 10a for an optical mask and a field stop 10b for an EUV mask. The field stop unit 10 can switch between the optical mask field stop 10a and the EUV mask field stop 10b according to the mask to be inspected.

The field stop 10a for optical masks is a plate-shaped member, and has slits 15a and 16a penetrating from one plate surface 11 to the other plate surface 12. The slits 15a and the slits 16a are, for example, rectangular when viewed from the direction orthogonal to the plate surface 11. For example, the slit 15a is smaller than the slit 16a and is inclined with respect to the slit 16a. The slit 15a transmits the illumination light L1a for autofocus, and the slit 16a transmits the illumination light L1a for inspection of the photomask Ma.

The slit 15a and the slit 16a are, for example, cavities. The field stop 10a for optical masks emits the illumination light L1a while maintaining the polarization state of the incident illumination light L1 including the linearly polarized light. Specifically, the illumination light L1a that has passed through the slit 15a and the slit 16a is emitted from the field stop 10a for the photomask while maintaining the polarization state. A portion of the illumination light L1a that has passed through the slit 15a is referred to as a beam B1a. A portion of the illumination light L1a that has passed through the slit 16a is referred to as a beam B2a. The polarization state of the beam B1a transmitted through the slit 15a and the beam B2a transmitted through the slit 16a are not changed. Therefore, the field stop 10a for photomasks emits the illumination light L1a having the beam B1a containing P-polarized light and the beam B2a containing P-polarized light.

The field stop 10b for EUV masks is a flat plate-like member, and has slits 15b, 16b and 17b penetrating from one plate surface 11 to the other plate surface 12. The slit 15b has the same shape as the slit 15a. The slit 16b and the slit 17b have the same shape as the slit 16a. The slit 16b and the slit 17b are arranged side by side. The slit 15b transmits the illumination light L1b for autofocus, and the slits 16b and 17b transmit the illumination light L1b for inspection of the EUV mask Mb.

A λ/4 plate is provided in the slit 15b. The illumination light L1b transmitted through the slit 15b is referred to as a beam B1b. The polarization state of the beam B1b that has passed through the slit 15b is changed to circularly polarized light.

Similar to the slit 16a, the slit 16b does not change the polarization state of the incident illumination light L1 and emits the illumination light L1b in the same polarization state. The illumination light L1b transmitted through the slit 16b is referred to as a beam B2b. Therefore, the beam B2b transmitted through the slit 16b contains, for example, P-polarized light.

A λ/2 plate is provided in the slit 17b. The illumination light L1b transmitted through the slit 17b is called a beam B3b. The beam B3b that has passed through the slit 17b has its polarization direction changed and contains S-polarized light.

As described above, the EUV field stop 10b includes the λ/2 plate and the λ/4 plate. The beam B1b includes a portion that transmits the λ/4 plate, and the beam B3b includes a portion that transmits the λ/2 plate. Therefore, the illumination light L1b transmitted through the EUV mask field stop 10b includes the circularly polarized beam B1b, the P-polarized beam B2b, and the S-polarized beam B3b. In this way, the EUV field stop 10b changes the polarization state of a part of the incident illumination light L1 including P-polarized light, and the beam B1b including circularly polarized light, the beam B2b including P-polarized light, and the beam B3b including S-polarized light. Illuminating light L1b having S-polarized light has a polarization direction different from that of P-polarized light.

As shown in FIG. 4, the illumination light L1 transmitted through the field stop unit 10 includes the illumination light L1a including the P-polarized beam B1a and the beam B2a, or the circularly-polarized beam B1b, the P-polarized beam B2b, and the S-polarized beam. The illumination light L1b includes the beam B3b. The illumination light L1 enters the beam splitter unit 20. The beam splitter unit 20 reflects at least a part of the illumination light L1. The beam splitter unit 20 can switch between a polarization beam splitter 20a for an optical mask (referred to as a PBS 20a for an optical mask) and a non-polarization beam splitter 20b (referred to as a non-polarization BS 20b).

The photomask PBS 20a reflects, for example, P-polarized light and transmits S-polarized light. For example, the photomask PBS 20a reflects the illumination light L1a including the P-polarized beam B1a and the P-polarized beam B2a that are incident through the photomask field stop 10a. The photomask PBS 20a reflects the illumination light L1a to the lower photomask Ma side. Further, the PBS for optical mask 20a transmits the reflected light R1a including the S-polarized light converted by the λ/4 plate 30 upward.

Specifically, the illumination light L1a incident on the photomask PBS 20a travels downward and is converted by the λ/4 plate 30 into illumination light L1a including the circularly polarized beam B1a and the circularly polarized beam B2a. Then, the illumination light L1a including the circularly polarized beam is condensed by the objective lens 40 and illuminates the photomask Ma.

FIG. 6A is a plan view illustrating the illumination light L1a that illuminates the pattern surface of the photomask Ma in the mask inspection apparatus 1 according to the embodiment. As shown in FIG. 6A, the illumination light L1a that illuminates the pattern of the photomask Ma includes a circularly polarized beam B1a and a circularly polarized beam B2a. A lens (not shown) may be arranged at a predetermined position on the optical path of the illumination light L1, and the lens and the objective lens 40 may constitute a relay optical system. Then, the field stop unit 10 may be arranged at a position conjugate with the mask to be inspected. By doing so, the intermediate projection image in the vicinity of the field stop unit 10 can be projected on the pattern surface of the mask to be inspected.

The reflected light R1a obtained by reflecting the illumination light L1a on the photomask Ma includes a circularly polarized beam B1a and a circularly polarized beam B2a. However, the reflected light R1a includes a circularly polarized beam that rotates in the opposite direction to the illumination light L1a. The reflected light R1a passes through the objective lens 40 and the λ/4 plate 30. At this time, the reflected light R1a including the circularly polarized beam B1a and the beam B2a is converted into the reflected light R1a including the S-polarized beam B1a and the beam B2a. The reflected light R1a including the S-polarized beam B1a and the beam B2a passes through the photomask PBS 20a.

The λ/4 plate 30 converts the illumination light L1a including the P-polarized beam B1a and the beam B2a into the illumination light L1a including the circularly-polarized beam B1a and the beam B2a. Further, the λ/4 plate 30 converts the reflected light R1a including the circularly polarized beam B1a and the beam B2a into the reflected light R1a including the S polarized beam B1a and the beam B2a.

The λ/4 plate 30 can be inserted into the optical paths of the illumination light L1a and the reflected light R1a. The λ/4 plate 30 is inserted in the optical paths of the illumination light L1a and the reflected light R1a when the optical mask Ma is inspected. The λ/4 plate 30 is removed from the optical paths of the illumination light L1b and the reflected light R1b when the EUV mask Mb is inspected.

The unpolarized BS 20b reflects a part of the illumination light L1b including the circularly polarized beam B1b, the P-polarized beam B2b, and the S-polarized beam B3b, and the circularly-polarized beam B1b, the P-polarized beam B2b, and the S-polarized beam B1b. Part of the reflected light R1b including the beam B3b is transmitted. For example, the non-polarized BS 20b is a non-polarized BS including a metal film. Therefore, the non-polarized BS 20b reflects a part of the illumination light L1b including the circularly polarized beam B1b, the P-polarized beam B2b, and the S-polarized beam B3b which are incident through the EUV mask field stop 10b. The non-polarized BS 20b reflects the illumination light L1b to the EUV mask Mb side below. The objective lens 40 focuses the illumination light L1b reflected by the non-polarized BS 20b on the EUV mask Mb. The objective lens 40 illuminates the EUV mask Mb with the collected illumination light L1b.

FIG. 6B is a plan view illustrating the illumination light L1b that illuminates the pattern surface of the EUV mask Mb in the mask inspection apparatus 1 according to the embodiment. As shown in FIG. 6B, the illumination light L1b that illuminates the pattern of the EUV mask Mb includes a circularly polarized beam B1b, a P-polarized beam B2b, and an S-polarized beam B3b. For example, the circularly polarized beam B1b, the P-polarized beam B2b, and the S-polarized beam B3b are sequentially illuminated from the +Y axis direction side to the −Y axis direction side on the pattern surface.

R1b reflected by the EUV mask Mb includes a circularly polarized beam B1b, a P-polarized beam B2b, and an S-polarized beam B3b. The objective lens 40 transmits the reflected light R1b obtained by reflecting the illumination light L1b on the EUV mask Mb. The non-polarized BS 20b transmits a part of the reflected light R1b that has passed through the objective lens 40 and that includes the circularly polarized beam B1b, the P-polarized beam B2b, and the S-polarized beam B3b.

The objective lens 40 focuses the illumination lights L1a and L1b reflected by the beam splitter unit 20 on the mask to be inspected. At the same time, the objective lens 40 transmits the reflected lights R1a and R1b, which are the illumination lights L1a and L1b reflected by the mask to be inspected.

The reflected light R1a has a beam B1a which is the beam B1a reflected by the photomask Ma and a beam B2a which is the beam B2a reflected by the photomask Ma. The reflected light R1b has a beam B1b in which the beam B1b is reflected by the EUV mask Mb, a beam B2b in which the beam B2b is reflected by the EUV mask Mb, and a beam B3b in which the beam B3b is reflected by the EUV mask Mb. In order to distinguish the beam B1a of the illumination light L1a and the beam B1a of the reflected light R1a, the beam B1a of the reflected light R1a may be referred to as the light B1a. The same applies to the other beams.

The mirror 50 reflects the reflected light R1 that passes through the objective lens 40 and the beam splitter unit 20 to the polarization splitting unit 60. The reflected light R1 is the reflected light R1a reflected by the photomask Ma or the reflected light R1b reflected by the EUV mask Mb.

The polarization splitting unit 60 splits the reflected light R1 that passes through the objective lens 40 and the beam splitter unit 20. The polarization splitting unit 60 includes a space splitting mirror 61. When inspecting the EUV mask Mb, the space division mirror 61 is arranged to reflect the S-polarized beam B3b located on the −Z axis side of the reflected light R1b.

A portion of the reflected light R1 on the +Z axis direction side does not enter the space division mirror 61, but passes through the space division mirror 61. For example, when inspecting the optical mask Ma, the S-polarized beam B2a located on the +Z axis direction side of the reflected light R1a passes through the space division mirror 61. When inspecting the EUV mask Mb, the P-polarized beam B2b located on the +Z-axis direction side of the reflected light R1b passes through the space division mirror 61 without entering the space division mirror 61.

The reflected light R1 reflected by the space division mirror 61 enters the detector 71. The reflected light R1 that has passed through the space division mirror 61 without being reflected by the space division mirror 61 enters the detector 72. In this way, the polarization splitting unit 60 guides the reflected light R1 transmitted through the objective lens 40 and the beam splitter unit 20 to the detector 71 and the detector 72.

In the case of the photomask Ma, the detector 71 or the detector 72 detects the reflected light R1a including the beam B2a transmitted through the objective lens 40 and the photomask PBS 20a.

In the case of the EUV mask Mb, the detector 71 detects the reflected light R1b including one of the beam B2b and the beam B3b that has passed through the objective lens 40 and the non-polarized BS 20b. Further, the detector 72 detects the reflected light R1b including the other of the beam B2b or the beam B3b that has passed through the objective lens 40 and the non-polarized BS 20b. The detectors 71 and 72 are, for example, TDI sensors.

The mask inspection apparatus 1 inspects the inspection target mask based on the reflected light R1 detected by the detectors 71 and 72. For example, the mask inspection apparatus 1 includes a processing unit (not shown) such as a PC (Personal Computer), and inspects an inspection target from an image processed using each reflected light detected by each detector.

FIG. 7 is a configuration diagram illustrating the autofocus unit 90a of the mask inspection apparatus 1 according to the embodiment, and shows a case of inspecting the optical mask Ma. As shown in FIG. 7, the autofocus unit 90a has a half mirror 91, a light receiving section 92, and a light receiving section 93.

When inspecting the optical mask Ma, the half mirror 91 transmits or reflects the autofocusing beam B1a that has passed through the objective lens 40 and the optical mask PBS 20a. The beam B1a transmitted through the objective lens 40 and the photomask PBS 20a contains S-polarized light.

The light receiving unit 92 is arranged, for example, at a position that serves as a front focus of an image formed by the beam B1a. The light receiving unit 92 receives, for example, the beam B1a transmitted through the half mirror 91. The light receiving unit 93 is arranged, for example, at a position where the image formed by the beam B1a is back-focused. The light receiving unit 93 receives, for example, the beam B1a reflected by the half mirror 91.

The autofocus unit 90a moves the objective lens 40 or the mask to be inspected by performing feedback control so that the beams B1a received by the light receiving unit 92 and the light receiving unit 93 have the same intensity. As a result, auto focus can be achieved.

FIG. 8 is a configuration diagram illustrating another autofocus unit 90a of the mask inspection apparatus 1 according to the embodiment. When switching the field stop unit 10 and the beam splitter unit 20, etc., a shift may occur between the front focus position and the rear focus position on the optical axis of the beam B1a for autofocusing. Therefore, as shown in FIG. 8, the autofocus unit 90a of the mask inspection apparatus 1 may include a correction unit that corrects the position of the front focus and the position of the rear focus.

The correction unit is, for example, the electric stage 8 that moves each light receiving unit and the slit. The slit is arranged on the light receiving surface of each light receiving unit. By the electric stage 8, each light receiving portion and the slit can be moved to adjust the position of the front pin and the position of the rear pin.

Further, the correction means is the positioner 9 arranged in the optical path of the beam B1a for autofocus. The positioner 9 includes a parallel plate that transmits the beam B1a. The positioner 9 is arranged immediately in front of the half mirror 91, for example. For example, the positioner 9 is arranged in the optical path between the half mirror 91 and the mirror 51 that reflects the beam B1a immediately before the half mirror 91. By adjusting the position and the inclination of the positioner 9, the optical axis shift can be corrected. The correction means is not limited to the stage 8 and the positioner 9. Further, the correction means may be provided in the autofocus unit 90b for inspecting the EUV mask Mb described below.

FIG. 9 is a configuration diagram illustrating the autofocus unit 90b of the mask inspection apparatus 1 according to the embodiment, and shows a case of inspecting the EUV mask Mb. As shown in FIG. 9, the autofocus unit 90b has a polarization means in addition to the half mirror 91, the light receiving section 92, and the light receiving section 93. The polarization means changes the polarization state of the beam B1b that has passed through the non-polarized BS 20b. The polarization means includes, for example, at least one of the polarization beam splitter 94 and the λ/4 plate 95. The polarization beam splitter 94 reflects S-polarized light and transmits other light. The λ/4 plate 95 converts circularly polarized light into S polarized light.

When inspecting the EUV mask Mb, the half mirror 91 transmits or reflects the beam B1b for autofocus that has passed through the polarization means. The beam B1b immediately after passing through the objective lens 40 and the unpolarized BS 20b contains circularly polarized light. On the other hand, the beam B1b that has passed through the polarization means contains S-polarized light.

The light receiving unit 92 is arranged, for example, at a position that serves as a front focus of an image formed by the beam B1b. The light receiving unit 92 receives, for example, the beam B1b transmitted through the half mirror 91. The light receiving unit 93 is arranged, for example, at a position where the image formed by the beam B1b is back-focused. The light receiving unit 93 receives, for example, the beam B1b reflected by the half mirror 91.

The autofocus unit 90b moves the objective lens 40 or the mask to be inspected by performing feedback control so that the beams B1b received by the light receiving unit 92 and the light receiving unit 93 have the same intensity. As a result, auto focus can be achieved. The autofocus unit 90b may also have a correction unit. The correction unit may be, for example, the electric stage 8 that moves each light receiving unit and the slit, as in the case of the autofocus unit 90a in the inspection apparatus for the photomask Ma, or may be arranged in the optical path of the beam B1b for autofocus. It may be the positioner 9.

<Mask inspection method>
Next, a mask inspection method for inspecting a mask to be inspected using the mask inspection apparatus 1 will be described. The mask inspection method will be described separately for the case of inspecting the optical mask Ma and the case of inspecting the EUV mask Mb. First, a method of inspecting the optical mask Ma will be described. FIG. 10 is a flowchart illustrating the case of inspecting the optical mask Ma in the mask inspection method according to the embodiment.

As shown in step S11 of FIG. 10, when inspecting the photomask Ma, the field stop unit 10 is switched to the photomask field stop 10a, and the beam splitter unit 20 is switched to the photomask PBS 20a. Further, the λ/4 plate 30 is inserted in the optical paths of the illumination light L1a and the reflected light R1a. Furthermore, it switches to the autofocus unit 90a for the photomask.

Next, as shown in step S12, the illumination light L1a is emitted through the photomask field stop 10a. Specifically, for example, the polarization state of a part of the incident illumination light L1 containing P-polarized light is changed, and the illumination light L1a having the beam B1a containing P-polarized light and the beam B2a containing P-polarized light is emitted. The illumination light L1a includes a beam B1a for autofocus and a beam B2a for inspection.

Next, as shown in step S13, the illumination light L1a emitted through the field stop 10a for photomasks is reflected by the PBS 20a for photomasks.

Next, as shown in step S14, the polarization state of the illumination light L1a is changed so that the illumination light L1a reflected by the photomask PBS 20a includes a circularly polarized beam. Specifically, the illumination light L1a is transmitted through the λ/4 plate 30 to convert the polarization state of P polarization into illumination light L1a having a circularly polarized beam B1a and a beam B2a.

Next, as shown in step S15, the illumination light L1a containing circularly polarized light is condensed on the photomask Ma by the objective lens 40, and the illumination light L1a reflected by the photomask Ma is collected by the objective lens 40. Glow. The reflected light R1a includes the beam B1a and the beam B2a reflected by the photomask Ma.

Next, as shown in step S16, the polarization state is changed so that the reflected light R1a includes an S-polarized beam. Specifically, the reflected light R1a is transmitted through the λ/4 plate 30 and converted into the reflected light R1a including the S-polarized beam B1a and the beam B2a.

Next, as shown in step S17, the reflected light R1a including the S-polarized beam B1a and the beam B2a is transmitted to the photomask PBS 20a.

Next, as shown in step S18, the focus is adjusted. Specifically, the beam B1a transmitted through the objective lens 40 and the photomask PBS 20a is transmitted and reflected by the half mirror 91. Then, the beam B1a that has passed through the half mirror 91 is received by the light receiving unit 92 that is arranged at a position that serves as a front focus of the image formed by the beam B1a. In addition, the beam B1a reflected by the half mirror 91 is received by the light receiving unit 93 arranged at a position to be a back focus of the image by the beam B1a. The position of the objective lens 40 or the mask Ma is adjusted based on the intensity of the beam B1a received by the light receiving unit 92 and the intensity of the beam B1a received by the light receiving unit 93. In this way, the focus of the reflected light R1a is adjusted.

Next, as shown in step S19, the reflected light R1a is detected. For example, an image of the pattern surface of the photomask Ma is acquired based on the reflected light R1a detected by the detector 72. In this way, the optical mask Ma can be inspected.

Next, a method of inspecting the EUV mask Mb using the mask inspection device 1 will be described. FIG. 11 is a flowchart illustrating the method for inspecting the EUV mask Mb in the mask inspection method according to the embodiment.

As shown in step S21 of FIG. 11, when inspecting the EUV mask Mb, the field stop unit 10 is switched to the EUV mask field stop 10b, and the beam splitter unit 20 is switched to the non-polarization BS 20b. The λ/4 plate 30 is removed from the optical paths of the illumination light L1b and the reflected light R1b. Furthermore, it switches to the autofocus unit 90b for the EUV mask.

Next, as shown in step S22, the illumination light L1b is emitted through the EUV mask field stop 10b. Specifically, for example, the polarization state of a part of the incident illumination light L1 including P-polarized light is changed, and a beam B1b including circularly polarized light, a beam B2b including P-polarized light, and a beam B3b including S-polarized light are included. The illumination light L1b is emitted. The illumination light L1b includes a beam B1b for autofocus, and a beam B2b and a beam B3b for inspection.

Next, as shown in step S23, the illumination light L1b emitted through the EUV mask field stop 10b is reflected by the unpolarized BS 20b. Specifically, a part of the illumination light L1b including the circularly polarized beam B1b, the P-polarized beam B2b, and the S-polarized beam B3b is reflected by the non-polarized BS20b.

Next, as shown in step S24, the illumination light L1b reflected by the non-polarized BS 20b is focused on the EUV mask Mb by the objective lens 40, and the reflected light R1b reflected by the EUV mask Mb on the illumination light L1b is reflected by the objective lens. The light is transmitted through 40 and condensed. The reflected light R1b includes the beam B1b, the beam B2b, and the beam B3b reflected by the EUV mask Mb.

Next, as shown in step S25, the reflected light R1b having the circularly polarized beam B1b, the P-polarized beam B2b, and the S-polarized beam B3b is transmitted to the non-polarized BS20b.

Next, as shown in step S26, the focus is adjusted. Specifically, the beam B1b transmitted through the objective lens 40 and the unpolarized BS 20b is transmitted and reflected by the half mirror 91. Then, the beam B1b that has passed through the half mirror 91 is received by the light receiving unit 92 that is arranged at a position that serves as a front focus of the image formed by the beam B1b. In addition, the beam B1b reflected by the half mirror 91 is received by the light receiving unit 93 arranged at a position to be a back focus of the image of the beam B1b. The position of the objective lens 40 or the EUV mask Mb is adjusted based on the intensity of the beam B1b received by the light receiving unit 92 and the intensity of the beam B1b received by the light receiving unit 93. In this way, the focus of the reflected light R1b is adjusted. It should be noted that when the half mirror 91 transmits and reflects the beam B1b, the beam B1b that has passed through at least one of the polarization means, for example, the polarization beam splitter 94 and the λ/4 plate 95 is changed to half. It may be transmitted and reflected by the mirror 91. As a result, the beam B1b can be S-polarized, and the reflectance with respect to the half mirror 91 can be improved.

Next, as shown in step S27, the reflected light R1b is detected. For example, the detector 71 detects the reflected light R1b including one of the beam B2b and the beam B3b. Further, the detector 72 detects the reflected light R1b including the other of the beam B2b and the beam B3b. As a result, an image of the pattern surface of the EUV mask Mb is acquired. In this way, the EUV mask Mb can be inspected.

Next, the effect of this embodiment will be described. In the mask inspection apparatus 1 of this embodiment, the autofocus beam B1a for illuminating the photomask Ma includes circularly polarized light. The beam B1b for autofocus that illuminates the EUV mask Mb also includes circularly polarized light. Therefore, the circularly polarized light can be used when the optical mask Ma and the EUV mask Mb are inspected by the same mask inspection apparatus 1. Therefore, since the polarization state of the light used for the autofocus unit 90 does not change due to the switching, the autofocus performance can be improved.

Further, when the beam B1a and the beam B1b for autofocus illuminate a pattern such as a line and space on the mask, the angle of the beam with respect to the pattern does not change by switching. As a result, even if the switching is performed, it is possible to prevent the stability of the autofocus from decreasing.

Further, S-polarized light is used as the beam B1a and the beam B1b which enter the half mirror 91. By using S-polarized light, it is possible to increase the reflectance with respect to the half mirror 191 and improve the autofocus performance. Therefore, the accuracy of mask inspection can be improved.

The mask inspection apparatus 1 can switch the field stop unit 10 and the beam splitter unit 20 according to the mask to be inspected. Therefore, the optical mask Ma and the EUV mask Mb can be inspected, and the inspection accuracy can be improved.

The mask inspection method using the mask inspection device 1 can inspect both the optical mask Ma and the EUV mask Mb with the same device. Therefore, the inspection cost and the inspection time can be reduced.

Although the embodiments of the present invention have been described above, the present invention includes appropriate modifications without impairing the objects and advantages thereof, and is not limited by the above-described embodiments. Further, the configurations in the embodiments may be appropriately combined.

1 Mask Inspection Device 8 Stage 9 Positioner 10 Field Stop Unit 11, 12 Plate Surfaces 15a, 15b, 16a, 16b, 17b Slit 20 Beam Splitter Unit 20a PBS for Optical Mask
20b Unpolarized BS
30 λ/4 plate 40 Objective lens 50, 51 Mirror 60 Polarization splitting unit 71, 72 Detector 80 Light source 90a, 90b Autofocus unit 91 Half mirror 92, 93 Light receiving unit 94 Polarization beam splitter 95 λ/4 plate 101a, 101b Inspection Apparatus 110a, 110b Field stop 115a, 115b CAF slits 116a, 116b, 117b Slit 120a Beam splitter 120b Non-polarizing beam splitter 130 λ/4 plate 140 Objective lens 151, 152 Mirror 190 Autofocus unit 191 Half mirror 192, 193 Light receiving part B1a , B1b, B2a, B2b, B3b Beams B101a, B101b, B102a, B102b, B103b Beams L1, L101, L101a, L101b Illumination light Ma Light mask Mb EUV masks R101a, R101b Reflected light

Claims (10)

A first beam including the first linearly polarized light and a second beam including a second linearly polarized light having a polarization direction different from that of the first linearly polarized light by changing a polarization state of a part of the incident illumination light including the first linearly polarized light And an EUV mask field stop that emits illumination light having a third beam including circularly polarized light,
A part of the light including the first linearly polarized light, the second linearly polarized light and the circularly polarized light is reflected, and a part of the light including the first linearly polarized light, the second linearly polarized light and the circularly polarized light is transmitted. A non-polarizing beam splitter,
While converging the illumination light reflected by the non-polarizing beam splitter on an inspection target mask, the first light reflected by the inspection target mask by the first beam and the second light reflected by the inspection target mask by the second beam An objective lens that transmits two lights and reflected light having the third light reflected by the mask to be inspected by the third beam;
A first detector that detects the reflected light that includes one of the first light and the second light that has passed through the objective lens and the non-polarizing beam splitter, and a second detection that detects the reflected light that includes the other A vessel,
A half mirror that transmits and reflects the third light transmitted through the objective lens and the non-polarization beam splitter;
A first light receiving unit that is disposed at a position that serves as a front focus of an image formed by the third light, and that receives the third light transmitted through the half mirror;
A second light receiving unit which is arranged at a position to be a back focus of the image by the third light, and which receives the third light reflected by the half mirror;
Mask inspection device. The field stop for the EUV mask includes a λ/2 plate and a λ/4 plate,
The second beam includes a portion that is transmitted through the λ/2 plate,
The third beam includes a portion that is transmitted through the λ/4 plate,
The mask inspection apparatus according to claim 1. Further comprising polarization means for changing a polarization state of the third light transmitted through the non-polarization beam splitter,
Transmitting and reflecting the third light through the polarizing means in the half mirror,
The mask inspection apparatus according to claim 1. The polarization means includes at least one of a polarization beam splitter and a λ/4 plate,
The mask inspection apparatus according to claim 3. For an optical mask that emits the illumination light having a fourth beam including the first linear polarization and a fifth beam including the first linear polarization while maintaining the polarization state of the incident illumination light including the first linear polarization. A field diaphragm unit capable of switching between a field diaphragm and the EUV mask field diaphragm;
A beam splitter unit capable of switching between the PBS for an optical mask which reflects the light including the first linearly polarized light and transmits the light including the second linearly polarized light, and the non-polarizing beam splitter.
A λ/4 plate insertable into the optical paths of the illumination light and the reflected light,
With
The mask inspection apparatus according to claim 1. When switching between the field stop unit and the beam splitter unit,
Further comprising a correction means for correcting the position to be the front pin and the position to be the rear pin,
The mask inspection apparatus according to claim 1. The correction means includes a first stage for moving the first light receiving portion and a slit arranged on the light receiving surface of the first light receiving portion, and a light receiving surface for the second light receiving portion and the second light receiving portion. It is a second stage that moves the arranged slit,
The mask inspection apparatus according to claim 6. The correction means is a positioner arranged in the optical path of the third light.
The mask inspection apparatus according to claim 6. A first beam including the first linearly polarized light and a second beam including a second linearly polarized light having a polarization direction different from that of the first linearly polarized light by changing a polarization state of a part of the incident illumination light including the first linearly polarized light And emitting illumination light having a third beam including circularly polarized light,
Collecting the illumination light on an inspection target mask by an objective lens, the first light reflected by the inspection target mask by the first beam, the second light reflected by the inspection target mask by the second beam, and Transmitting the reflected light having the third light reflected by the mask to be inspected by the third beam to the objective lens;
Transmitting and reflecting the third light of the reflected light transmitted through the objective lens at a half mirror;
A step of receiving the third light transmitted through the half mirror by a first light receiving portion arranged at a position that becomes a front focus of an image formed by the third light;
A step of receiving the third light reflected by the half mirror by a second light receiving part arranged at a position to be a back focus of the image by the third light;
The position of the objective lens or the inspection target mask is adjusted based on the intensity of the third light received by the first light receiving unit and the intensity of the third light received by the second light receiving unit. Steps,
Focus adjustment method with. In the step of transmitting and reflecting in the half mirror,
Causing the third mirror to transmit and reflect the third light through a polarization unit that changes the polarization state of the third light;
The focus adjusting method according to claim 9.